Our earlier U.K. Patent Application No. 9419372.9 (2 282 209A) describes locking devices which can be used with a rotatable component such as a shaft or a tube. Although such devices achieve a reliable locking function, a collar means of the device tends to tilt when the device is locked in position and hence wobbles when the shaft or tubes revolves. A general object of the present invention is to provide an improved form of locking device which overcomes this defect.